events: Introduce PlatformEventDispatcher and PlatformEventSource.

ui/events/platform/platform_event_dispatcher.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_EVENTS_PLATFORM_PLATFORM_EVENT_DISPATCHER_H_
+#define UI_EVENTS_PLATFORM_PLATFORM_EVENT_DISPATCHER_H_
+
+#include "base/basictypes.h"
+#include "ui/events/events_export.h"
+#include "ui/events/platform/platform_event_types.h"
+
+namespace ui {
+
+// See documentation for |PlatformEventDispatcher::DispatchEvent()| for
+// explanation of the meaning of the flags.
+enum PostDispatchAction {
+  POST_DISPATCH_NONE = 0x0,
+  POST_DISPATCH_QUIT_LOOP = 0x1,
+  POST_DISPATCH_PERFORM_DEFAULT = 0x2,
+  POST_DISPATCH_STOP_PROPAGATION = 0x4,
+};
+
+// PlatformEventDispatcher receives events from a PlatformEventSource and
+// dispatches them.
+class EVENTS_EXPORT PlatformEventDispatcher {
+ public:
+  // Returns whether this dispatcher wants to dispatch |event|.
+  virtual bool CanDispatchEvent(const PlatformEvent& event) = 0;
+
+  // Dispatches |event|. If this is not the default dispatcher, then the
+  // dispatcher can request that the default dispatcher gets a chance to
+  // dispatch the event by setting POST_DISPATCH_PERFORM_DEFAULT to the return
+  // value. If a nested message-loop is active, then the dispatcher can signal
+  // that the nested message-loop should be terminated by setting
+  // POST_DISPATCH_QUIT_LOOP flag on the return value. If the dispatcher has
+  // processed the event, and no other dispatcher should be allowed to dispatch
+  // the event, then the dispatcher should set POST_DISPATCH_STOP_PROPAGATION
+  // flag on the return value.
+  virtual uint32_t DispatchEvent(const PlatformEvent& event) = 0;
+
+ protected:
+  virtual ~PlatformEventDispatcher() {}
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_PLATFORM_PLATFORM_EVENT_DISPATCHER_H_